1. Field of the Invention
The invention pertains to the field of baseband radar systems and more particularly to means for beam narrowing and target angle measurement with baseband radar systems.
2. Description of the Prior Art
Systems employing subnanosecond baseband pulses for object detection generally exhibit beam widths that are too broad for the effective discrimination of angularly displaced targets. Conventionaly, angular resolution is achieved in the radar system by the utilization of narrow beam antennas. However, these antennas have relatively narrow frequency bands and antennas that are broadband enough to propagate subnanosecond pulses also have an inherently broad beam width. Where it is desired to detect targets within about five feet from the antenna, the inherent broad beam widths produced by baseband antennas are not a particular problem because the outer boundary of the range gate and the natural fall off of the antenna response severely restricts the area covered at the shorter range. For some distances beyond this range, signal processing techniques have been sUccessfully employed to narrow the effective beam widths. One such technique has been described in U.S. Pat. No. 3,858,205 issued Dec. 31, 1974 to Ross and assigned to the assignee of the instant invention. However, these techniques become virtually ineffective when the range to the target becomes very large compared to the transmitter-receiver spacing.
It is difficult to obtain a system that exhibits both a narrow effective beam width and negligible signal dispersion (i.e., a wide band width). In antenna array systems, for example, one can obtain a narrow beam by employing a multiplicity of elements and making the aperture dimensions many wavelengths. However, to simultaneously obtain a wide bandwidth it is necessary to employ real time delays in the element feed network rather than instantaneous phase shift behind each element to afford coherent addition at the appropriate sum port.
This invention describes a novel method for achieving a narrow effective beam width, for a baseband radar system, in which only two receiving antennas are employed and wherein the system effectIve beam width is directly proportional to the pulse width of the received signals.